1. Field of the Invention
The present invention relates to a thermally assisted magnetic recording head, and it particular relates to a magnetic circuit used for recording.
2. Description of the Related Art
Recently, in a magnetic recording device typified by a magnetic disk apparatus, in association with high recording density, there is a demand for improvement in performance of thin film magnetic heads and magnetic recording media. As the thin film magnetic head, composite-type thin film magnetic heads are widely used in which a reproducing head having a magneto-resistive effect element (MR element) for reading, and a recording head having an induction-type electromagnetic transducer element for writing, are laminated on a substrate.
The magnetic recording medium is a discontinuous medium where magnetic grains are aggregated, and each magnetic grain has a single magnetic domain structure. Each recording bit on the magnetic recording medium is configured by a plurality of magnetic grains. In order to increase the recording density, asperities at the border between adjacent recording bits need to be decreased by decreasing the size of the magnetic grains. On the other hand, decreasing the size of the magnetic grains, i.e., decreasing in the volume of the magnetic grains, results in a decrease in the thermal stability of magnetization in the magnetic grains. In order to resolve this problem, it is effective to increase the anisotropic energy of the magnetic grains. However, the increased anisotropic energy of the magnetic grains enhances the coercive force of the magnetic grains, making it difficult to record the information on an existing magnetic head.
As a method for resolving this problem, a so-called thermally assisted magnetic recording is proposed. In this method, a magnetic recording medium with a high coercive force can be used. At the time of recording information, the simultaneous addition of a magnetic field and heat to a portion of the recording medium where the information increases the temperature of that portion. This results in information being recorded by the magnetic field at the portion where the coercive force is decreased. Hereafter, the magnetic head used for thermally assisted magnetic recording is referred to as a thermally assisted magnetic recording head.
In thermally assisted magnetic recording, a near-field light (NF light) is used in general as a means for adding heat to the magnetic recording medium. The NF light is a type of electromagnetic field formed around the periphery of a material, and is not restricted by a diffraction limit due to light wavelength. As a result, it is possible to focus light onto a very small domain on the order of tens of nm.
A thermally assisted magnetic recording head using an NF light is described in US2010/0103553. A magnetic circuit that applies a magnetic field to a magnetic recording medium extends with a roughly U-shape within a plane that is orthogonal to an air bearing surface (ABS) of the magnetic head and the substrate, and a magnetic flux is emitted from the recording front end part that is one end of the U-shape, and the magnetic flux is absorbed from the other end. An NF light generator is positioned inside the U-shape within the plane, i.e. between both ends of the magnetic circuit when viewed in the down track direction (recording medium circumferential direction). In order to place the portion that is heated by the NF light on the magnetic recording medium and the portion where the magnetic flux is emitted as close as possible, the NF light generator is positioned close to the recording front end part in the down track direction.
Since the NF light generator is close to the recording front end part of the magnetic circuit, the light that is generated by the NF light generator is transmitted to the magnetic circuit, and the recording front end part is heated by this light. In order to enhance the magnetic flux density, a cross section that is orthogonal to the ABS of the recording front end part is generally small. Consequently, as the front end part is heated to a high temperature, it causes damages to itself, and to a dielectric body, such as Al2O3 and the like, covering the periphery of the magnetic circuit, abnormal deformation of the NF light generator and the generation of cracks. Further, the damage or omission of a protective layer made of diamond like carbon (DLC) and the like that protects the ABS occurs, which also causes a collision between the magnetic recording medium and the magnetic head.
The objective of the present invention is to provide a thermally assisted magnetic recording head that easily prevents heating of the recording front end part by heat from the NF light generator.